Who says you have to? Both the DualShock 3 and 360 pad, and maybe even the new console controllers, work great with most Android devices. There are also Android specific solutions like the MOGA controllers.
Also, Amazon, the company offering this deal, has something that might work and was recently launched. It's probably not a coincidence.
To add to this discussion, buying a Fire TV and controller is a pretty slick deal right now, for customers dropping the $140 on the Fire TV + Controller you'd get (or be able to get):
1. The Fire TV
2. The Game Controller
3. Sev-0, the game we made
4. 1,000 Coins for buying the controller
5. You could then use those 1,000 Coins to get GTA: San Andreas for free
6. You could then use your 2,000 additional Coins to get $20 in additional games